diff --git a/prometheus/prometheus.go b/prometheus/prometheus.go
index a12a7bb..1032eba 100644
--- a/prometheus/prometheus.go
+++ b/prometheus/prometheus.go
@@ -8,22 +8,32 @@ import (
 )
 
 func InstrumentService(s http.HandlerFunc) (handler http.HandlerFunc) {
-	counterVec := p.NewSummaryVec(p.SummaryOpts{
+	requestDuration := p.NewSummaryVec(p.SummaryOpts{
 		Namespace: "gotsrpc",
 		Subsystem: "service",
 		Name:      "time_nanoseconds",
 		Help:      "nanoseconds to unmarshal requests, execute a service function and marshal its reponses",
 	}, []string{"package", "service", "func", "type"})
-	p.MustRegister(counterVec)
+	requestSize := p.NewSummaryVec(p.SummaryOpts{
+		Namespace: "gotsrpc",
+		Subsystem: "service",
+		Name:      "size_bytes",
+		Help:      "request and response sizes in bytes",
+	}, []string{"package", "service", "func", "type"})
+
+	p.MustRegister(requestSize)
+	p.MustRegister(requestDuration)
 
 	return func(w http.ResponseWriter, r *http.Request) {
 		*r = *gotsrpc.RequestWithStatsContext(r)
 		s.ServeHTTP(w, r)
 		stats := gotsrpc.GetStatsForRequest(r)
 		if stats != nil {
-			counterVec.WithLabelValues(stats.Package, stats.Service, stats.Func, "unmarshalling").Observe(float64(stats.Unmarshalling))
-			counterVec.WithLabelValues(stats.Package, stats.Service, stats.Func, "execution").Observe(float64(stats.Execution))
-			counterVec.WithLabelValues(stats.Package, stats.Service, stats.Func, "marshalling").Observe(float64(stats.Marshalling))
+			requestSize.WithLabelValues(stats.Package, stats.Service, stats.Func, "request").Observe(float64(stats.RequestSize))
+			requestSize.WithLabelValues(stats.Package, stats.Service, stats.Func, "response").Observe(float64(stats.ResponseSize))
+			requestDuration.WithLabelValues(stats.Package, stats.Service, stats.Func, "unmarshalling").Observe(float64(stats.Unmarshalling))
+			requestDuration.WithLabelValues(stats.Package, stats.Service, stats.Func, "execution").Observe(float64(stats.Execution))
+			requestDuration.WithLabelValues(stats.Package, stats.Service, stats.Func, "marshalling").Observe(float64(stats.Marshalling))
 		}
 	}
 }